1. Field of the Invention
The present invention relates to a heat-developable photosensitive material and an image forming method using the photosensitive material, and particularly to a heat-developable photosensitive material suitable for medical diagnosis, industrial photographs, and COM, and to a heat developing method using the same.
2. Description of the Related Art
In recent years, there has been a strong desire for decreasing the amount of waste from the viewpoint of environmental protection and space saving in the medical diagnosis film fields and photographic plate-making film fields. As a result, technologies for heat-developable photosensitive materials that are used for medical diagnosis films and photographic plate-making films, which can be efficiently exposed using a laser-image setter or a laser imager, and can form a distinct black image having high resolution and definition, are required. According to the heat-developable photosensitive material, a heat developing system which requires no solution type processing chemical, and which is simple and does not damage the environment, can be supplied to customers.
Though in the general field for image forming materials there is the demand, images for medical diagnosis especially require high image qualities having excellent definition and granularity, because fine drawings are required for medical diagnosis. Further, images having a cold black tone tend to be preferred from the viewpoint of medical diagnostic easiness. At present, a variety of hard copy systems utilizing pigments and dyes such as ink jet printers and electrophotographs are distributed as general image forming systems. However, none of these systems is satisfactory as the output system of medical images.
On the other hand, a heat image forming system utilizing an organic silver salt is described in, for example, respective specifications of U.S. Pat. Nos. 3,152,904 and 3,457,075 and in B. Shely, “Thermally Processed Silver Systems” (Imaging Processes and Materials), Neblette, No. 8 edition, edited by J. Sturge, V. Walworth and A. Shepp, page 2, 1996.
Particularly, a heat-developable photosensitive material generally has a photosensitive layer comprising a reducing agent, a reducible silver salt (e.g., organic silver salts), a photocatalyst (e.g., silver halide), in an amount to be active as a catalyst, and as required, a color tone controlling agent for controlling the tone of the silver. These materials are dispersed in a binder matrix in the layer. The heat-developable photosensitive material is heated at a high temperature (for example, 80° C. or more) after image exposure, and a silver image having a black color is formed by an oxidation-reduction reaction between the reducible silver salt (functions as an oxidizer) and the reducing agent. The oxidation-reduction reaction is facilitated by the catalytic action of a silver halide latent image generated by exposure. Accordingly, the silver image having a black color is formed in the exposed region. The heat-developable photosensitive material is disclosed in many documents such as U.S. Pat. No. 2,910,377 and Japanese Patent Application Publication (JP-B) No. 43-4924. Further, the Fuji Medical Dry Imager FM-DP L, which is a medical image forming system using a heat-developable photosensitive material, has been put on the market.
In a heat type image forming system utilizing an organic silver salt, there is a method in which production is carried out by applying a solvent, and a method in which production is carried out by applying a coating solution containing polymer fine particles comprised as a main binder and dispersed in water, followed by drying. The latter method does not require the steps of recovering the solvent and the like. Therefore, production equipment for the latter method is simple, and the method is advantageous for mass-production.
The image forming system utilizing an organic silver salt does not include a fixing step. Therefore, the system has a large problem concerning image preserving ability after developing, particularly, concerning deterioration of the printout when exposed to light after development. As a method for improving deterioration of the printout, a method utilizing AgI, which is formed by converting an organic silver salt, is disclosed in U.S. Pat. No. 6,143,488 and EP No. 0,922,995. However, such a method in which the organic silver salt is converted using iodine as disclosed in the above cannot obtain sufficient sensitivity and it is difficult to form an actual system.
In addition, there are descriptions concerning photosensitive materials utilizing AgI in WO 97-48014, WO 97-48015, U.S. Pat. No. 6,165,705, Japanese Patent Application Laid-Open (JP-A) No. 8-297345, Japanese Patent No. 2785129 and the like. However, none of these photosensitive materials can attain a sufficient level of sensitivity and fogging and is fit for practical use as a photosensitive material to be exposed with a laser. Therefore, the development of a method in which a silver halide containing a large content of silver iodide can be used has been desired.